Boris Johnson is to take personal charge of the future of the Olympic Park after moving the chairman of the London Legacy Development Corporation to a new role after just four months in the job.

Daniel Moylan, a former deputy chairman of Transport for London, will now lead the mayor's aviation review. The move has been criticised by London assembly members, who say it exposes a crucial lack of planning experience at the top of the organisation.

It is understood there have been tensions between Moylan and some members of the LLDC board over key decisions, including the future of the Olympic Stadium and the cavernous media centre.

The LLDC has found tenants for seven of the eight permanent venues and is in negotiations with West Ham for the football club to become the main tenant in the stadium, which will be shared with UK Athletics, a concert promoter and other sports. It has promised to reach a conclusion by October.

Insiders said there had been a "clash of styles" between Moylan and some members of the board. "Securing the future of the Olympic and Paralympic legacy and building on the regeneration of east London is a matter of huge importance to me personally," said Johnson.

"It is vital that I continue to be at the forefront of the decision-making, driving forward the huge task of delivery. The chairmanship of the LLDC will enable me to do just that, building on what has already been achieved."

Margaret Ford, the former chair of the LLDC's predecessor, the Olympic Park Legacy Company, was told by Johnson to step aside several months early once she had decided to leave so that Moylan could assume the role.

Moylan, seen as one of Johnson's key lieutenants, ousted chief executive Andrew Altman and appointed the chief executive of the Olympic Delivery Authority, Dennis Hone, as an interim replacement.

"I have worked with Boris for two years now to bring London's pressing need for a new hub airport to the top of the political agenda. The 2012 Games have shown that Britain can deliver major projects better than anyone if it has the will to do so," said Moylan.

"A new hub airport to the east of London would be the greatest legacy we could create for London and the country at large. That is why I have accepted the mayor's invitation to put the majority of my time into aviation. The time for action is now and we need to bring the government round to that view.

"I have had the huge privilege of chairing the Legacy Corporation for the last three months, working with its dedicated staff and getting to know the fantastic, enthusiastic and wonderful people of Stratford and the nearby areas. I give up the post with a heavy heart, but knowing that, alongside aviation, the mayor intends to make this one of the great priorities of his second term and is demonstrating this by taking the chairmanship of the Legacy Corporation himself."

Darren Johnson, a Green party assembly member, said it was important that the mayor appointed senior planning figures to take the 20-year plan forward.

The north end of the park is due to reopen on 27 July next year, with the south end – including the stadium – reopening in spring 2014.

"I am worried that Olympic Park legacy will become a bog-standard mix of concrete and tarmac unless the mayor immediately appoints some senior people who have real experience of delivering an imaginative regeneration project," said Johnson.

"He recently lost two of the key people in charge of the project. He also appointed Daniel Moylan against the advice of the London Assembly's confirmation panel, who criticised Mr Moylan's lack of regeneration experience. London expects an amazing legacy to follow an amazing Olympics and Paralympics. I hope the mayor will take the assembly's advice."